Process for making wet-strength paper and product thereof

ABSTRACT

A PAPER WEB CONTAINING 1-20 PRECENT OF A THERMOSETTING RESIN SUCH AS PHENOL OR UREA FORMALDEHYDE AND 0.1-4 PRECENT OF A CHROMIUM COORDINATION COMPLEX OF A FLUOROHYDROCARBON WHICH IS DISSOLVED IN A SOLVENT IS IMMERSED IN A BATH OF MOLTEN WAX. FROM 5-40% OF THE WAX IS PICKED UP ON THE PAPER WEB; THE HEAT OF SAID WAX ALSO HELPS TO CURE THE THERMOSETTING RESIN. THE FLUOROHYDROCARBON IS ADDED TO THE WEB CONTAINING THE RESIN AT ANY STAGE IN THE PAPERMAKING PROCESS PRIOR TO THE WAX IMPREGNATION. THE FLUOROHYDROCARBON ADDITION GENERALLY IMPARTS TO THE PAPER WEB THE ABILITY LIMIT THE WAX PICK-UP AND CONTROLS ITS DISTRIBUTION ON THE PAPER WEB.

1971 G. s. scARvEus 3,556,930

PROCESS FOR MAKING WET-STRENGTH PAPER AND PRODUCT THEREOF Filed Feb. 29,1968 INVENTOR. GUS SSCNWE \9.

United States Patent PROCESS FOR MAKING WET-STRENGTH PAPER i Int. Cl.D21f 11/00 US. Cl. 162-135 3 Claims .ABSTRACT OF THE DISCLOSURE A paperweb containing 1-20 percent of a thermosetting'resin such as phenol orurea formaldehyde and 0.1-4 percent of a chromium coordination complexof a fluorohydrocarbon which is dissolved in a solvent is immersed inabath of molten wax. From 5-40% of the wax is picked up on the paperweb; the heat of said wax also helps to cure the thermosetting resin.The fluorohydrocarbon isadded to the web containing the resin at anystage inthe papermaking process prior to the wax impregnat on. Thefluorohydrocarbon addition generally imparts to the paper web theability to limit the wax pick-up and control its distribution on thepaper web.

I BACKGROUND OF THE INVENTION 1 This invention is concerned with awet-strength paper which generally contains a thermosetting resin, 21fluorohydrocarbon, and a wax impregnated portion.

More specifically, this invention is concerned with a paperestructurewhich contains a thermosetting resin, a fluorohydrocarbon and a waximpregnation wherein the heat of the molten wax impregnation is used tocure the thermosetting resin and the fluorohydrocarbon is used tocontrol the wax pick-up.

-Wet-strength papers are generally known in the prior art. Likewise, theaddition of waxes and thermosetting resins to paper compositions toimprove their wet-strength properties is commonly known in the art.However, the prior are wet-strength papers,'wherein a wax is used incombination with a thermosetting resin, are disadvantageous .in that thefold qualities of the paper are often adversely affected, and theresulting paper product tends to have .a dirty, brown color as a resultof the wax impregnation. t a

The fold qualities-ofa paper product are extremely important in-thatpaper, when used as a packaging medium,.must,=be folded to form. usefularticles, such as boxes, cartons, etc. In the formation of thesearticles, it is conventional' to .score the paper and to subsequentlyapply mechanicalpressure to the paper in such a way that it folds on thescore line.,If the paper is extremely brittle du'e.19..chemicaljreatment, for example, treatment to impart water-resistant properties,the paper will tend to crackas opposed to bending evenly on the scoreline. In accordance with this invention, this problem is overcome.

Likewise, the outward appearance of the paper product is extremelyimportant in that the general appearance of thepapei tends" to' relay animage to the recipient or customer as to the contents contained inarticles made from the paper. This appearance factor isparticularlyimporta'nt'in the'wet-strength paper area as large quantities of wetstrength paper are used to form food containers. It is iinperativethat acontainer relay immediately to the recipient or customer animage'ofcleanliness. The dirty brown" containers ".of the. prior art are notcapable of conveying this imageofcleanliness. In order'to overcome thisdirty, brown color, whcih was generally inherent in the prior art, it.is often common to pigment the paper surface in such a way as to whitensaid surface. By

ice

means of the subject invention, a wet-strength paper having outstandingfolding qualities and excellent color is obtained, without the use of apigment, thereby eliminating the problems of the prior art.

The primary object of this invention is a superior paper product havingoutstanding foldability properties.

Another object of this invention is superior paper which has outstandingwet-strength properties.

Still another object of this invention is a paperboard sheet havingsuperior aesthetic properties.

The objects of this invention also include the process whereby thesuperior paper of this invention is produced.

Finally, the objects of this invention include all the other novelfeatures in the specification and claims at hand.

The paper product as produced in accordance with this invention isgenerally illustrated in the cross-sectional view as shown in thedrawing.

The resulting paper product 2 generally comprises a. fibrous cellulosicweb 4 which contains a thermosetting resin. The upper extremities offibrous web 4 are impregnated with a fiuorohydrocarbon to form animpregnated layer which is illustrated as layer 6. Layer 6 is likewiseimpregnated with a wax material. However, note specifically that the waximpregnation, hence the color of the resulting product, is carefullycontrolled by the fluorohydrocarbon addition. If desired, the resultingproduct can contain a slight wax overlay.

As is stated above, this invention is concerned with a paperboard sheetwherein the cellulosic substrate is treated with a thermosetting resin,a fluorohydrocarbon, and a wax impregnation.

The paper substrate of this invention can be formed from anyconventional cellulosic material.

Cellulosic materials adapted for use in this invention include woodcellulose and pulps derived from hardwoods, softwoods, and woody annualplants such as balsam fir, Eastern hemlock, jack pine, Eastern whitepine, red pine, black spruce, red spruce, white spruce, tamarack,cyprus, quacking aspen, American beech, paper birch, yellow birch,Eastern cottonwood, sugar maple, silver maple, yellow poplar, 'blackcherry, white oak, bagasse, hemp, cotton and jute. Mixtures ofcellulosic materials can also be used.

The preferred paper substrate for use in accordance with this inventionis kraft paper which is produced from Southern pine.

As is commonly known in the art, cellulosic materials as described aboveare converted into a useful paper web or sheet by a paper-making processsuch as the Fourdrinier process. In the Fourdrinier process, a slurry ofcellulosic fibers is converted into a wet sheet which is subsequentlydried, calendered, etc., to produce a continuous paper web.

Prior to the formation of this continuous web, the cellulosic fibers,while in a slurry form, are mechanically agitated in what is generallydescribed as a beater. This beating step fibrillates and frees thefibers in such a way that they are susceptible to web formation. Thethermosetting resin as used in this invention can be applied at anyconvenient point in the paper-making process. However, it is preferredin this invention that the thermosetting resin be applied in the beatingstage of pulp preparation. The thermosetting resin is generally added ina powdered or slurry form to the cellulosic fibers just prior toheating. The beating mixes the thermosetting material with the fibers insuch a way that a desirable homogeneous mass is formed. The resultingthermosetting resin-fibrous mixture is then diluted to a convenientpaper-making concentration and is delivered onto the continuously movingwire belt in such a way as to form a continuous wet sheet. This wetsheet is then dried and calendered in a conventional manner.

The cellulosic mixture can contain from about 0.5 to about 20 percent ofthermosetting resin. A more preferred range for the thermosetting resinis from about 5 to about 15 percent. The most preferred concentration isabout percent. The above percentages are based on the Weight of the drycell-ulosic fibers utilized.

Any thermosetting resin which is compatible with cellulosic materialscan be, utilized in accordance with this invention. Examples of suitablethermosetting resins are phenol formaldehyde resins, urea formaldehyderesins, melamine resins, alkyd resins, polyamide resins and acrylateresins, etc.

Subsequent to the formation of a cellulosic web, which contains athermosetting resin as described above, the web is dried and calenderedin a conventional manner. In accordance with this invention, afluorohydrocarbon is added to the thermosetting resin-containing web atsome stage prior to the drying of the paper product in question. Inaccordance with the most preferred aspect of this invention, thefluorohydrocarbon is added subsequent to the first calendering stagealthough it is understood by one skilled in the art that thefiuorohydrocarbon can be added at any stage in the paper-making processprior to the wax impregnation. Specifically, it should be noted that thefluorohydrocarbon can be added during the heating stage or just prior tothe formation of the wet sheet. The addition of the fluorohydrocarbonsubsequent to web formation is extremely advantageous in that it ispossible to concentrate the fluorohydrocarbon in the surface portion ofthe web in such a Way as to maximize its usefulness.

From about 0.1 to about 4.0 percent of fluorohydrocarbon can be used inaccordance with this invention. A more preferred range offluorohydrocarbon is from about 0.2 to about 3.0 percent, with the mostpreferred concentration of the fluorohydrocarbon being about 2.0. Theabove concentrations are based on the dry weight of the paper web inquestion. Fluorohydrocarbons which are adapted for use in accordancewith this invention generally have a polar head, which can interact withcellulose, and a non-polar fluorocarbon tail, which is both organophobicand hydrophobic.

Fluorohydrocarbons which are adapted for use in accordance with thisinvention are generally chromium coordination complexes of afluorochemical dissolved in a solvent such as isopropyl alcohol, whichcontain about 3 percent chromium, or aqueous solutions of water solublefluorochemicals. Complexes of this type are generally disclosed in U.S.Pats. Nos. 2,662,835; 2,642,416; 2,713,- 593; and 2,934,450.

Examples of specific fluorohydrocarbons which can be used in accordancewith this invention, and which fall within the above-described genericdefinition, are Scotchban FC-805, which is a solution of a chromium saltof a fatty acid in which some of the hydrogen has been replaced withfluorine, such as perfluorocaprylic acid, as sold by the 3 M Company ofMinneapolis, Minn.

The most preferred fluorohydrocarbon for use in accordance with thisinvention is the above-described FC-805 product. This product isgenerally disclosed in U.S. Pat. No. 2,662,835 issued to Reed, and isproduced by reacting chromyl chloride with a saturatedperfluoromonocarboxylic acid having from four to twelve carbon atoms inthe molecule, such as perfiudro-octanoic acid, in an inert anhydrous orsolvent vehicle and in the presence of an alcohol reducing agent or ahydrolyzed ammoniated derivative thereof.

The above-described fiuorohydrocarbon addition generally imparts to thepaper web in question the ability to control wax pick-up. This abilityis extremely important if a resulting paper product having a desirableappearance is to be produced. For example, if too much wax isimpregnated in the paper in question, the paper tends to have a dirtybrown color which makes it unsuitable for use in the food trade.

In accordance with this invention, it is possible to carefully limit thewax pick-up and control its distribution'on the paper substrate, withthe result that a paper having desirable aesthetic qualities can beproduced.

The fl-uorohydrocarbon addition in accordance with this.

invention is likewise extremely useful in that it tends to make theresulting paper greaseproof. These greaserepelling properties are notlost, even subsequent to wax impregnation. This property is extremelydesirable in containers which are used for the shipment of fatty meatswhich have a tendency to give paper products a greasy, dirty appearance.

Subsequent to the treatment of the paper web with the fiuorohydrocarbon,the paper product is exposed to a molten wax bath. This wax impregnationcan be accomplished at any convenient time. If the resulting paperproduct is to be used in a straight sheet form, the Wax impregnation cantake place in the papermaking sequence just prior to the finalcalendering operation. However, if the resulting paper product is to beconverted into corrugated board, it is advantageous to form thecorrugated board prior to the wax addition. This procedure is desirablebecause the wax impregnation tends to make the gluing of the linermaterials to the corrugated Web difiicult. In contrast, if the Waximpregnation is accomplished afterthe corrugated board is formed, thesedifficulties are not encountered.

The wax impregnation can be from about 5 to about 40 percent. A morepreferred range for the wax impregnation is from about 10 to about 30percent by weight. The most preferred concentration for the waximpregnation is about 20 percent. Examples of suitable waxes which canbe used in accordance with this invention are microcrystalline andparaflinic Waxes. Synthetic Waxes, such as those based on aliphaticmolecules, such as polyethylene, polypropylene, etc., can also be usedin accordance 'with this invention. Mixtures of waxes can also be used.The general melting point for waxes for use in accordance with thisinvention is from about to about 200 F.

As is stated above, the wax impregnation in accordance with thisinvention is accomplished by immersing the thermosetting resin andfluorohydrocarbon-contairiing paper material in a bath of molten wax.The heat of the molten wax is then utilized to effect a curing of thethermosetting resin. While the wax bath can be at any convenienttemperature, the temperature should be suflicient to cure thethermosetting resin utilized to the desired degree in the resultingproduct. For use in most applications, a temperature range of from about200 F. to about 300 F. can be utilized. Amore preferred range is fromabout 225 F. to about 250 F. The most preferred embodiment of thisinvention is a kraft web which is impregnated with 10 percent of phenolformaldehyde resin and 2 percent of FC-SOS fluorohydrocarbon. Thiscombination is subsequently impregnated and cured by immersing in a bathof paraffin wax at a temperature of 250 F.

In is within the purview of this invention to add to the compositions ofthis invention compatible materialswhich do not affect the basic andnovel characteristics of the composition of this invention. Among suchmaterials are coloring agents, including dyes and pigments, fillers, andsimilar additives. Additives such as antioxidants, antistatic agents,stabilizers and anti-foaming, may also be added. The upper limit of thequantity of additives is usually about 1 weight percent of the product.

The following examples will illustrate the subject invention. Theseexamples are given for the purpose of illustration and not for purposesof limiting this invenwise specified.

EXAMPLES 1-5 Examples 1 to 5 were prepared and tested in accordance withthe following description:

Southern kraft liner pulp was refined in the laboratory Mead refiner to450 Canadian Standard Freeness, dewatered, fluffed, bagged and moisturedeterminations made.

A solution of a urea formaldehyde resin sold under TAB LE I Fluorohydro-Percent carbon Percent the trade name, Amres 1430, was prepared withwater as the solvent medium.

Fifty (50) grams of pulp (ovendry basis) were diluted to 10 liters.Enough Amres solution to give 5 grams of.

active Amres was added to the slurry and the mix was agitated forcomplete mixing. This Amres-treated pulp was then ready for handsheetmanufacture.

Each handsheet contained 5.2 grams of pulp (ovendry basis) and was madein a Williams sheet mold using standard procedures. The 7" x 7" sheetswere pressed for five (5) minutes at 150 p.s.i. and dried in a Noble andWood drum drier. Pressing and drying were done between blotters.

A 1 percent solution of Scotchban FC-SOS was prepared. After thehandsheets to be treated with Scotchban were manfactured and dried, the1 percent solution was poured onto the sheets on a level surface. Theexcess Scotchban was then squeezed off the sheets by rolling a stainlessrod (Meyers rod) over the surface. The sheets were then re-dried on theNoble and Wood drum drier. The sheets were then immersed in the meltedwax and then run through a hand squeegee to remove excess wax. The waxedsheets were air-dried.

In Examples 1-5, a 26 lb. sheet was prepared.

The brightness of the samples produced was tested in accordance withtest ASTM D985-50.

The fold endurance of the resulting product was tested in accordancewith TAPPI Test No. T423 m-50.

In testing the grease resistance, 1" x 2" samples were cut. One squareinch of the specimen was completely covered with vegetable oilshortening sold under the trademark Crisco. The samples were then placedin a room at 80 F.35% RH for a period of 72 hours. After the 72 hours,the samples were taken from the 80 F.35% RH room and the amount ofgrease penetration and the amount of grease wicked onto the uncoatedareas were observed.

The data for Examples 1-5 is expressed in Tables I and II:

Modifications may be resorted to within the spirit and scope of theappended claims.

What is claimed is:

1. As an article of manufacture, a fibrous paper product having improvedwet-strength containing 1-20 percent of thermosetting resin uniformlydistributed among the fibers, 0.1-4 percent of a chromium coordinationcomplexof a fluorohydrocarbon, and having a surface impregnated with5-40 percent wax.

2. As an article of manufacture, a paper product comprising a fibrouspaper web containing approximately 10 percent of phenol formaldehyderesin uniformly distributed among the fibers and which containsapproximately 2 percent of a chromium coordination complex of afiuorohydrocarbon, and the surface portions of said Web are impregnatedwith approximately 20 percent of paraffin wax, said percents by weightbased upon the dry weight of said paper.

3. A process for forming a paper product which comprises the steps offorming a fibrous paper web containing 1-20 percent of a thermosettingresin uniformly distributed among the fibers, applying 0.1-4 percent ofa chromium coordination complex of a fluorohydrocarbon dissolved in asolvent to said web, and immersing the resulting paper web in a moltenwax bath.

References Cited UNITED STATES PATENTS 2,868,685 1/1959 Downs 117-923,402,068 9/1968 Wilkins 11792 3,109,769 11/1963 Martin 162-182 OTHERREFERENCES Casey: Pulp and Paper, vol. II. Interscience Publishers,Inc., N.Y., 1960 (p. 947).

S. LEON BASHORE, Primary Examiner R. H. ANDERSON, Assistant Examiner US.Cl. X.R.

